There are today numerous medicament delivery devices on the market where the main intention is to use them for self-administration of medicament. The patient or user should thus be able to use the device, whereby the device should be easy and intuitive to use for a wide range of patients from children to elderly as well as persons with reduced dexterity of the hands.
In many instances it is an advantage that different doses may be set individually by the user. This could for example be that a user should take different doses during a medication period or that the same device could be used for different persons requiring different doses, such as children and adults requiring different quantities of medicament.
It could also be an advantage that the force member, such as a spring, which is acting on a medicament container in order to expel a dose, is tensioned when a dose is set. In this way the device does not have to be stored in a highly tensioned state as often is the case with devices using spiral compression springs. Thus, the risk of damage to the devices due to creeping effects in the materials of the device is greatly reduced.
With this type of function some devices have been utilizing strip spiral springs, or clock springs, that are wound in a spiral having a central passage in which a hub is placed. Document WO 2008/155144 discloses a medicament delivery device arranged with a strip clock spring. The spring is arranged transversal in relation to the longitudinal direction of the device and is tensioned by turning a knob at the distal end of the device. When a dose of medicament is to be delivered an actuation button at the proximal end of the device is depressed whereby the clock spring is released to rotate a plunger rod, whereby the latter is moved in the proximal direction, acting on a stopper in a medicament container, such a dose of medicament is expelled.
This type of spring is particularly advantageous when the medicament has a high viscosity since such a spring usually can produce higher forces than ordinary compression springs. This type of spring is also more easily tensioned just prior to medicament dose delivery than other types of springs. However, the drawback with this type of spring is that it gives the medicament delivery device a rather large diameter at least where the spring is situated, since it is positioned transversal to the longitudinal direction and since it requires a number of windings. The thickness increases further if an activation button is to be placed in the distal end of the device. Therefore most devices with such springs have the activation button in the proximal end of the device, which sometimes is not advantageous.